...Ligeia Mare is about the same size as Lake Huron and Lake Michigan combined.

"Before Cassini, we expected to find that Ligeia Mare would be mostly made up of ethane, which is produced in abundance in the atmosphere when sunlight breaks methane molecules apart," says Le Gall.

"Instead, this sea is predominantly made of pure methane."

Her study is based on data collected with Cassini's radar instrument during flybys of Titan between 2007 and 2015 and combines several radar observations of heat given off by the sea as well as data from a 2013 experiment that bounced radio signals off it.

That 2013 experiment sent back echoes from the seafloor giving an indication of the sea's depth – 160 metres at its deepest point.

Le Gall and her colleagues used the data to get an idea of what the composition of the sea and the seabed might be.

"We found that the seabed of Ligeia Mare is likely covered by a sludge layer of organic-rich compounds," she says.How different organic compounds make their way to the seas and lakes on Titan, the largest moon of Saturn – ESA

This tallies with what we previously knew about the moon. Nitrogen and methane react in the atmosphere to produce a wide variety of organic materials, the heaviest of which are believed to fall to the surface.

Le Gall's study suggests that when these compounds reach the sea some are dissolved in the liquid methane while the insoluble ones, such as nitriles and benzene, sink to the sea floor.

The study found that the shoreline around Ligeia Mare may be porous and sodden with liquid hydrocarbons. The scientists deduced that by measuring temperature changes between spring and summer. Unlike on Earth, they recorded little change between the temperature of the land and the sea, suggesting that the land is so filled with hydrocarbons, it changes temperature at much the same rate.

"It's a marvellous feat of exploration that we're doing extraterrestrial oceanography on an alien moon," said Steve Wall, deputy lead of the Cassini radar team at NASA's Jet Propulsion Laboratory in California.

......Liquid methane and ethane flowing through Vid Flumina, a 400-kilometre river often compared to the Nile River, is fed by canyon channels running hundreds of metres deep.

ut during this pass, the radar was used as an altimeter, sending pings of radio waves to the moon's surface to measure the height its features.

The timing of the radar echoes bouncing off the canyons' edges and floors gave the Cassini team a direct measure of their depths.

The researchers combined the altimetry data with previous radar images of the region to make their discovery and proposed scenarios for the deep cuts, such as terrain uplift and changes in sea level – or perhaps both.

"It's likely that a combination of these forces contributed to the formation of the deep canyons, but at present it's not clear to what degree each was involved," says Valerio Poggiali of the University of Rome and lead author of the study.

The reason I'm posting it here is because he accepts the claim that oil is abiotic in origin, which means that it is produced within the Earth and is thus replenished over time, though not as fast as it's being extracted. He only discusses that briefly toward the end. But it's interesting anyway that the U.S. is apparently now the top producer of oil and maybe natural gas and coal too.